Wednesday, December 4, 2013

Reverse total shoulder - what about lengthening of the arm?

These authors reviewed seven articles bearing on the issue of arm lengthening after reverse total shoulder arthroplasty. They found that changes in humeral length varied from minus five to five millimetres, and changes in upper-extremity length varied from 15 mm to 27 mm. Humeral and arm shortening increased the risk of dislocation and led to poor anterior active elevation. From this literature review the authors concluded that deltoid tensioning by restoring humeral length and increasing the acromiohumeral distance is critical for adequate postoperative function and to prevent dislocation. They caution against excessive arm lengthening to avoid postoperative neurological impairment.

The amount of lengthening resulting from a reverse depends on the preoperative position of the arm, the superior-inferior position of the glenosphere on the glenoid, the presence or absence of eccentricity of the glenoid component, the size of the glenoid component, position of the humeral component in the humeral bone, and the design of the humeral cup (including shell height and polyethylene thickness). The authors estimate that these factors potentially allow arm lengthening by up to several centimeters (about 10 % of arm length).

There is no easy answer to "how much should the arm be lengthened by a reverse total shoulder?" Some shoulders having reverse total shoulders are chronically contracted in an upward position while others are very lax. The issues of presurgical pathoanatomy, bone quality, stability, arm lengthening, neurologic injury, function, acromial fractures, and prosthesis design are interrelated and complex. As an example one of the cases in this article had a preoperative acromial fracture making it difficult to tension the deltoid; the shoulder dislocated after surgery, but this problem could not have been prevented by increasing the lengthening of the arm. Furthermore, trying to achieve stability by tensioning the deltoid with the arm at the side does not provide stability when the arm is passively abducted away from the side (a position that reduces the deltoid tension). Lateral ("East-West") tensioning of the shoulder in addition to moving the arm distally ("South" tensioning) may provide more stability throughout the range of motion and reduce the risk to the acromion and brachial plexus from a distally tight reconstruction. The change in position of the humerus relative to the scapula depends on both the prosthesis design and the placement of the glenoid and humeral components in their respective bones.

Our practice is to carefully assess and discuss with the patient the bone structure, the bone quality, the residual cuff integrity, the neurological status and the joint laxity before surgery. At surgery, we attempt to balance the soft tissues and to achieve stability by East-West as well as South tensioning, avoiding over-tensioning the deltoid to minimize the risk of nerve damage and acromial fracture. Radiographic measurements of the amount of lengthening are helpful in clinical research, as shown by this review paper.